The present invention relates generally to handheld power tools, and specifically to combustion-powered fastener-driving tools, also referred to as combustion tools.
Combustion-powered tools are known in the art, and one type of such tools, also known as BUILDEX® brand tools for use in driving fasteners into workpieces, is described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722; 5,197,646; 5,263,439 and 6,145,724, all of which are incorporated by reference herein. Similar combustion-powered nail and staple driving tools are available commercially from ITW-Paslode of Vernon Hills, Ill. under the IMPULSE®, BUILDEX® and PASLODE® brands.
Such tools incorporate a tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces a spark for ignition, and a fan located in a combustion chamber provides for both an efficient combustion within the chamber, while facilitating processes ancillary to the combustion operation of the device. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a single cylinder body.
Upon the pulling of a trigger switch, which causes the spark to ignite a charge of gas in the combustion chamber of the engine, the combined piston and driver blade is forced downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original, or pre-firing position, through differential gas pressures within the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
Conventional combustion fastener driving tools employ two types of fuel delivery systems, mechanical fuel injection and electronic fuel injection. With mechanical fuel injection, the fuel cell is provided with a metering valve, either affixed to the fuel cell or to the tool. The fuel cell is inserted into a fuel cell chamber of the tool with the bottom of the fuel cell facing generally towards the workpiece when the tool is oriented operationally. Once a fuel cell door is closed, formations on the door and/or internal linkages cause the fuel metering valve to dispense a measured quantity of fuel to the tool's combustion chamber.
When electronic fuel injection is employed, the delivery of fuel is controlled by a central processing unit (CPU) typically incorporating a microprocessor. In such configurations, the fuel cell is inserted into the fuel cell chamber in the opposite orientation relative to the mechanical fuel injection configuration. As such, the fuel cell is inserted with the dispensing end toward the tool's nosepiece. Once inserted, the fuel cell stem is sealingly engaged or coupled to a fuel injector controlled by the CPU.
When a combustion tool is operated in cold weather, cold fuel is fed from the fuel cell into the engine. Partial or complete interruption of the fuel flow can occur when vapor is formed in the fuel-feeding system, causing vapor lock. Thus, combustion tools typically incorporate a heating system in order to preheat the fuel. Conventionally, the fuel cell is placed parallel to the engine to absorb the heat transferred from the engine. However, the fuel cell is often placed a distance away from the engine as a safety precaution to separate the flammable fuel from the engine. The fuel cell may also be separated from the engine by a cover, housing partitions or other housing components. Although the safety reasons for separating the fuel cell from the engine are sound, the configuration also prevents the amount of heat transferred from the engine to the fuel cell, and may not be effective for preventing vapor lock in cold weather conditions.
In other prior art heating systems, such as when the electronic fuel injection is employed, a fuel line used to transmit the fuel from the injector to the combustion chamber is run parallel to the engine to capture the radiant heat from the engine. However, like the other prior art tools, the fuel line is placed a distance from the engine and may be separated by an engine cover, similar to the above discussion of the fuel cell, which results in relatively poor heat transfer. Additionally, the fuel line also has a very small cross-section and only a relatively small portion of the fuel is preheated at one time.
Another problem with prior art fuel cells is that they are permitted to rotate in the tool. While the fuel cell is designed to retain the fuel unless drawn by the tool, rotation of the fuel cell may lead to an increased likelihood of fuel leaks.
Thus, there is a need for a combustion-powered fastener-driving tool and fuel cell which address the problem of sufficiently preheating the fuel.
Further, there is a need for a combustion-powered fastener-driving tool and fuel cell which address the problem of fuel cell rotation in the tool.